1. Field of the Invention
The present invention relates to an optical polarizer having a prism for an optical isolator.
2. Description of the Prior Art
Optical isolators are employed in optical communications technology for suppressing back-reflections of the optically transmitted flux in the direction back to the semiconductor laser used as a radiation source and/or transmitter. Such back-reflections may be caused, for example, by connectors, splices, discontinuites, and the like. Experiments have shown that the stability of the laser emission can be disrupted even when the difference between the emitted and the reflected radiant power is as low as 40 decibels.
Consequently, the isolation of the optical isolator must be as high as possible in order to achieve stable operation of the laser. Conventional optical isolators used for this purpose generally consist of a Faraday rotator placed between two polarizers crossed at 45.degree. as described in the article "Microoptic Grating Multiplexers and Optical Isolators for Fiber-Optic Communications," K. Kobayashi and M. Seki, IEEE Journal of Quantum Electronics, Vol. QE-16, No. 1, January 1980, pages 11-22. In order for the optical isolator to achieve a high degree of isolation, the polarizer facing the semiconductor laser should not produce any back-reflections, and further should exhibit a high degree of polarization.
The use of such a device as an optical polarizer disposed at the input side of an optical isolator has already been proposed. Such a polarizer is in the form of a polarization beam splitter and consists of two prisms which are separated from one another by a multilayer dielectric structure. Such a proposal is described in the article "Ein Kontinuierlich Einstellbarer Laserstrahl-Abschwacher Aus Dielektrischen Vielfachschichten," by H. F. Mahlein and W. Rauscher, Optic 38, Vol. 2, 1973 pages 187-195.